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Does talcum powder cause cancer? Let the jury decide…

Talcum powder has been in the dock recently. Johnson & Johnson have lost a $417 million lawsuit launched against them by a woman who claimed that the company’s ‘Baby Powder’ product caused her to develop ovarian cancer. The claim is that the company deliberately hid information linking ovarian cancer to using talcum powder in the groin area. J&J claim that there is nothing to hide that talcum powder is safe to use, and will be appealing the decision.

“Talc causes cancer” – as far as headlines go, I’ve heard less alarming ones. But it is true? What’s the evidence behind this?

Some perspective on powder

An increased risk of a third sounds like a lot. But – bear in mind ovarian cancer is an awful disease but it is thankfully rare. In response to a 2016 lawsuit, the charity Target Ovarian Cancer point out that for a woman with no family history of ovarian cancer, her lifetime risk is 2% – putting this into perspective, about 4 out of 200 women will develop ovarian cancer, but if all those women use talc, this will rise to only about 5 out of 200 women – an extra one woman in 200:

How many additional women without a family history of ovarian cancer will develop the disease if they use talc? Source for lifetime risk statistics: Cancer Research UK

The International Agency for Research on Cancer classes talcum powder as a ‘possible carcinogen’ (cancer-causing thing) – which put it in the same category as pickled vegetables, petrol, and aloe vera. Think about how worried you are about getting cancer from one of those items.

Is baby powder for babies?

So far we’ve been talking about talcum powder putting women at risk of ovarian cancer. But what about baby girls?

As far as I can see at least, there have been no studies looking specifically at whether talc use puts babies at a particularly increased risk of ovarian cancer in later life. One might assume that starting talc use earlier in life might have more of an effect, because it means that woman is ‘exposed’ to talc for longer. But actually the evidence doesn’t bear that out – even in studies which suggest an increased risk, there is no correlation between how long someone uses talc for, or how much they use at a time, and the amount their risk is increased by. Which, if you think about it, is a bit weird, if talc is meant to be a cancer causing product.

The jury’s verdict is in…

So, does talc cause cancer or not? As you might have gathered – it’s complicated. There are lots of subtleties and unanswered questions. And it’s entirely possible that there will never be a definitive black-and-white answer – the public could be living in a grey area for the foreseeable future.

And yet Johnson & Johnson are losing lawsuits left right and centre, with hundreds more lawsuits waiting for them (potentially more than 1,500, according to one organisation, funded by a law firm actively seeking plaintiffs.)

Courtrooms operate on coming to certain definitive answers, and skilled lawyers exploit uncertainty to their own advantage – or to the disadvantage of their opposition. For that reason I’m not convinced that the courtroom is the best forum for answering questions like this.

You could argue that the courtroom forces someone to make the decision that dithering scientists in their ivory towers cannot. But it’s two different games that are being played.

In the courtroom, evidence is selectively chosen to put the strongest case forward, in order to ultimately win a case. Finding a ‘truth’ that everyone has faith in relies upon the opposing team putting the opposite case forward using their best evidence – because that’s balance, right? – and then hopefully a group of 12 lay people in the middle can make sense of it all.

But science doesn’t work in this way. In an ideal world, the scientific method is one that examines all the evidence and judges each piece on it’s own merit – analysing it in some systematic way, and then coming to a conclusion based on probabilities, not certainties. Yes, scientists disagree all the time on things, but they don’t settle debates by suing each other.

I’m sorry that the women who brought these cases got ovarian cancer – it’s a truly awful disease, and I hope that they have found some solace in the results of their lawsuits.

But cases like this reinforce a myth that that the courts can answer the questions that science cannot – this unhelpful for the public, undermines evidence-based health information, and will do nothing on it’s own to tackle ovarian cancer.

Explainer – how do scientists link talc to cancer?Firstly, I’ll focus on human studies and ignore lab-based or animal studies. Partly because I haven’t got the time/energy to delve into lab studies, but mostly because the main criticism of using evidence from such studies is that they’re not studies in real humans. And I think that’s fair enough – I doubt the public cares whether talc causes cancer in mice, or causes cells to grow faster in a Petri dish. They want to know whether talc causes cancer in actual real people.

So how do you find that out? Well, broadly, there are three main ways to test stuff on humans:

Randomised controlled trial: take two groups: one group is sprayed every day with talcum powder, and the other is not, and then you wait and see whether one group develops more cancers than the other. This is an appropriate method of testing whether a medicine cures a disease, but obviously impractical and completely unethical for testing whether talc – or anything, for that matter – causes cancer.

Retrospective observational studies – in a ‘case-control’ study, you get a group of people who have developed ovarian cancer, and a group of people who haven’t, and you ask them about their talc usage in the past. This is reasonable effort, and is the most common way these kinds of studies are done. However, one of the main criticisms levelled at these studies is that they rely on people’s memories of what they did. To illustrate, answer this question: Have you ever regularly used talcum powder on your body or your underwear, for at least once per month for any amount of time?This an actual question from an actual study which found a link between talc and ovarian cancer – do you think you could give a reliable answer? There’s also the possibility of something called ‘Recall bias’ – in short, a woman who has ovarian cancer might remember more readily that she used talc – compared to someone who didn’t get ovarian cancer – as she could be trying to rationalise why she developed the disease.

Prospective observational studies – you gather a large group of women, none of whom have ovarian cancer. You follow them around for a long time, typically a decade or more. You regularly ask them their current talc use habits (and probably a few other things, otherwise it’d be a bit weird). Unfortunately, it’s inevitable that some of these women will develop ovarian cancer over time – but since you know more precisely how much talc they use during the study time (you’re not relying upon their memory) you can work out whether talc had anything to do with their ovarian cancer, all other things being equal. These kinds of studies are as close to a randomised controlled trial as it’s possible to get. The problem is that they’re incredibly difficult to get rolling and maintain, and it might be decades before you get any significant results, so there aren’t many of them.

So what have these different studies found?

Some retrospective studies have found a moderate increase in risk of ovarian cancer, whilst others have not. Two separate ‘meta-analyses’ of lots of these studies together show an increased risk of 24% and 33%. However, two prospectivestudies show no effect of talcum powder. Hence it’s a bit of a mixed bag.